Pushing back front caliper piston

I am in the middle of my first pads and rotors replacement on my 92 GS. After removing the drivers side front rotor today, I noticed the piston on the caliper was almost all of the way out (while caliper was supported on top of dust shield near control arm, because I didnt remove the banjo bolt where the brake line enters the caliper so it was still attached). I went to push the caliper back in and my finger slipped, and the piston fell out of the caliper dust boot completely, spilling brake fluid everywhere. I cleaned up the mess and removed the banjo bolt from the caliper so I could take it off the car and work on getting the piston back in easier. With some needle-nose pliers and a friend I was able to slightly stretch the caliper dust boot open enough to slide the piston back in. I was able to manually (by hand) push the piston back in about 2/3 of the way, where it abruptly stopped and refused to go any farther in. Not sure if it was in all the way, I got a c-clamp to try and force it in a bit more (read that this is an acceptable way of pushing the piston back in when doing pads). However, the piston still wouldnt budge at all.

Here are some pictures, is this piston back in as far as it can go? If not, any helpful hints on how to get it back in all the way? Thanks

Just replace the caliper. Same thing happened to me a a week ago. My caliper locked up on me and my brakes felt like shit. When I went to replace the front pads and rotors the piston on the driver side caliper would not budge even with a c-clamp. Luckily I had a spare caliper at home so I didn’t pay for anything.(Autozone lifetime warraty brakes and rotors)

Thats definately the surefire way to “fix” it and the easy way out, but Im looking to see if theres anything I can do before that step.

Ive even seen rebuild kits on rock auto (or somewhere similar) for like 7 dollars a side for these Nissin calipers, and it wouldnt be beyond me to rebuild it myself if it came down to it.

Thanks for the input and story, and I will replace if completely necessary but looking for ideas/reasoning in the meanwhile.

is it stuck?? can you pull it out and try again or is it jammed in tight? if its in tight… forget it buy a new one because at the very least you have scored the piston wall and it will leak when u do get it unstuck.

Are you putting pressure on that one point with the clamp? From what I can see you may have it jammed sideways. You may want to try a larger clamp with a small piece of wood to sit on the rim of the piston so it will distribute the load evenly. The piston should be able to go flush with the caliper. Looks like you may have close to an inch to go.
I see the hose is off so its not hydraulic pressure holding the piston back. You can get new pins, sleeves, bolts, clips, a piston and all the seals for fairly cheap. Rockauto is my cars savior. You will need a small cylinder hone that attaches to a drill. Its a $20 tool that will resurface the inside of the caliper where the piston slides. http://www.sears.com/shc/s/p_10153_12605_00999291000P?vName=Tools&cName=MechanicsTools&sName=Automotive%20Specialty%20Tools&psid=FROOGLE01&sid=IDx20070921x00003a

Or you could be like me by saying screw it and spend $34 a piece for rebuilt front calipers. I got them from Advance without pads or the brackets. Oh and take the old ones in, the core charge is $50 each these days ($100 ouch). Since its all broken down you may want to consider caliper paint as well. Its cheap and easy bling.

Good luck.

take the piston back out and clean the walls. the part that goes in the caliper.

you could get a rebuild kit but unless there is some deep scoring on the walls then you should be able to re-use your old pistons in the mean time.

and probably see if any local parts store carries the dust boot.

I can pull it back out, it isnt completely stuck, just wont go down any further.

At that one point with the clamp I suppose I was putting pressure on just one point, but it wasnt budging either way and before then I had pushed it down evenly with my hands. I doubt the sides of the piston are scored too badly. Good idea with the block of wood and a larger clamp, I just hope I have a bigger one around somewhere.

34$ after core for rebuilt calipers isnt bad at all, good to know I have that option if it comes down to it… I was thinking more like 75+ each but maybe that was without cores.

Yeah I think I will take the piston back out, clean it off some and check for scoring, clean out the walls of the caliper, lube everything up nicely and try again. I dont think I would need a new dust boot, as the one I have now is unripped and works fine.

It may just be having a hard time going back in because a good amount of grease came off the piston over the course of me messing with it.

So being unhooked from the brake line (no fluid or hydro pressure), the piston ideally should slide all the way back in until its flush pretty easily?

Whats the best kind of grease/oil I should use to lube it back up? Or will any generic oil made for this type of thing work.

Thanks for the help!

There is no reason to use a clamp with the line removed. It will push in by hand. Did you clean everything before puuting it back together?

Looked pretty clean (no debris etc) but obviously now that was a mistake not wiping everything off and relubing.

Will take apart after work, wipe down piston and interior cylinder wall of caliper, lube up with some silicon grease and smear some brake fluid over piston, and put it back in the caliper. Hopefully this is all thats needed and it’ll slide all the way back in… dont really see why it wouldnt work :cross:

here is a trick to try to make it easier though.

put the piston in the freezer for 30 min or so… then take it out and put it in.

Good idea, to contract the metal a hair so it would slide in easier

Ended up messing with it some more and got it to somehow go in without even taking the piston back out. Think I’m all set, thanks everyone

next time, use your old brake pad and the c-clamp to push it back in.